Horizontal sealing of the base slab

Hello!

Now I would be interested in your opinion again.
In about 1 week the pouring for the screed will take place (plumbers and electricians are currently busy). Now the following issue has come up:

- We have no horizontal sealing on the floor slab (no basement) and the screed installer has now pointed out to us that this apparently does not comply with the standard

- We have no horizontal sealing because the builder said that this is not necessary since we have a capillary-breaking barrier of 40 cm (Geocell foam glass gravel). This was also recorded in the awarding protocol and in the construction meeting protocols

- The non-necessity was also confirmed by the architect with a building physics calculation, which is also documented in the construction meeting protocols

=> Our issue now is, for example, what the insurance says in case of a pipe burst. Can they refer to the standard and possibly pay less in case of damage, even though the non-necessity was confirmed by our professionals?

Here again the structure (as mentioned, no basement, so directly on the ground):

200 mm gravel
400 mm foam glass gravel (capillary-breaking)
200 mm concrete
110 mm EPS granulate
70 mm cement screed
10 mm tiles

What do you think? Absolutely seal it anyway?

Best regards
Jochen

Hello,

it is almost certain that it works without the welding membrane on the base plate. The insurance will always refer to the recognized rules of technology, so there could be a problem there. But I lack the imagination for such an insurance case. Pipe break under the base plate? I don't know...

My imagination sometimes runs away with me

At this point, only a spray bitumen coating of about 3 mm is possible, and this is applied to all the pipes. Doesn’t it then provide some sealing against the floor structure?

Floor slabs that are installed in contact with the ground and above which rooms with superior usage are expected (these are living spaces) must be sealed against rising moisture!
Capillary-breaking layers such as gravel and foam glass gravel (the latter, by the way, an excellent thermal insulation) do not prevent the water vapor transport through the concrete.
Concrete can be installed as watertight concrete (WU concrete), but that has nothing to do with water vapor diffusion!
Water vapor will always follow the physical rules of vapor pressure gradient. Under ground-contacting floor slabs, we always empirically assume a high humidity. In the rooms above, there will always (!) be a lower water vapor pressure.
So the water vapor "marches" through the concrete into the living space and tries, following the physical rules, to balance the lower humidity against the higher.
That means:
Regardless of whether gravel lies beneath the floor slab or not, the humidity in the rooms will always be high, and mold formation will be an unwanted constant partner in the house without any possibility of limiting it in the future.
I am not a fan of "stirring up fears"! I also view the mold problem rather unemotionally. But with the planned construction of the floor slab without waterproofing, it is clear to me what is to be expected here for you in the near future.
My suggestion:
Submit written concerns and insist on waterproofing on the floor slab, take photos of the construction progress as evidence.
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Regards: KlaRa

Thank you for your detailed and understandable explanation. It is probably really more about the steam issue and not, for example, a possible pipe break. In another forum, someone also raised the issue of radon exposure. However, we are here in radon potential class 1.

The whole matter is too risky for me and I don’t want to risk anything here. In the end, we would have the problem and the impact would be relatively large compared to the costs. Therefore, we will now apply such a spray sealant on the base plate and the laid pipes before the filling comes. Better safe than sorry!

Thanks anyway for your inputs!

Best regards